The Substitute (1993)

After high school teacher Gayle Richardson finds out her husband is cheating on her, killing him and his mistress in an outburst of rage, she sets the house on fire and flees. One year later we find her back in another town, at another school, under another name. Everything is running smoothly, until people start messing with her new life and her hidden past and she is forced to stop them... at all costs.